Modern hard disc drives comprise one or more rigid discs that are coated with a magnetizable medium and mounted on a spindle hub of a spindle motor for rotation at a high speed. Information is written to and read from tracks on the discs through the use of an actuator assembly, which rotates during a seek operation. A typical actuator assembly includes a plurality of actuator arms. The actuator arms extend toward the discs. One or more flexures extend from each of the actuator arms. Mounted at the distal end of each of the flexures is a read/write head. The read/write head is affixed to a fluid-bearing slider that enables the read/write head to fly in close proximity above the corresponding surface of the associated disc. The fluid can be air or alternatively an inert gas, such as, but not limited to, helium. As rotational velocity of the disc decreases, the layer of fluid supporting the slider above the disc surface diminishes and the slider, and thus the read/write head, descends toward the disc surface. Contact between the slider/head assembly and the disc surface can damage the magnetizable medium and the read/write head.
Storage capacity of a hard disc drive may be increased by increasing the number of tracks per inch (TPI) on discs in the disc drive. In order to increase TPI, however, it is necessary to decrease the magnetic spacing between a read/write head and active magnetic layers deposited on the surface of the corresponding disc. This magnetic spacing includes a carbon coating on the read/write head, pole tip recession, gap fly height, a carbon overcoat deposited over the active magnetic layers and lubricant deposited over the carbon overcoat. Gap fly height is a measurement that represents the distance between a read/write head and the lubricant deposited over the carbon overcoat on the corresponding disc.
Due to increasing TPI, gap fly height is significantly decreasing. Indeed, future products may have a gap fly height of lower than 0.5 microinches. Depending on variability in manufacturing and design processes, increasing TPI in disc drives may force sliders into intermittent or even continuous contact with the surface of the corresponding disc. Many disc drive manufacturers are thus limited with respect to the amount of storage capacity that may be realized by increasing TPI.